digs for a temperature-monitoring device buried more than two feet underground.
Photos by Jerry Lower/The Coastal Star
By Cheryl Blackerby
Is replacement sand on beaches affecting sea turtle gender?
That’s a question county environmentalists will try to answer in a study of three county beaches — Boynton Beach Oceanfront Park, Jupiter Beach, which has three types of replacement sand, and Singer Island.
The temperature of beach sand affects the sex of sea turtle eggs. Sand 84 degrees or higher is more likely to produce females and below 84 degrees is more likely to produce males.
Since temperatures of replacement sand vary depending on where the sand came from, county environmentalists are worried that renourishment projects may be altering the delicate balance of gender determination.
“South Florida nests produce mostly female turtles,” said Kelly Martin, an environmentalist with Palm Beach County Environmental Resources Management. “That’s good but there’s a fine line.”
The project was started in April to determine whether sand dredged from offshore, which is darker and hotter, and mined inland sand, which is paler and cooler, have an effect on turtle gender. Temperature-monitoring devices buried in the sand will remain until October.
All of the sand used on South County beach renourishment projects has been dredged sand except for a dune project in Delray Beach.
“There was mined sand put on the beach in South Palm Beach for many years, but our last project there was in 2010 and that sand has been eroded,” said Leanne Welch, shoreline program supervisor for ERM.
Most reptiles including alligators, crocodiles, turtles and lizards lay eggs that depend on temperature for gender determination.
But turtle sex determination is the opposite of lizards and crocodiles, Welch said. “Warmer temperatures produce more female turtles, but more male lizards and crocodiles.”
On a recent August morning, Martin scooped out big handfuls of sand at the Boynton Beach Oceanfront Park beach, reached down 18 inches, and pulled out a monitor that logs the temperature of the beach sand every 15 minutes.
She dug deeper and retrieved another monitor 27 inches deep, the depth on the beach that green turtles and leatherbacks bury their eggs. Loggerheads lay their eggs at 18 inches.
Six monitors were placed on Oceanfront Park beach, and 30 at the other two beaches. Martin checks each monitor once a month and records the data with the help of Lory Gort, a biology student intern from Palm Beach Atlantic University.
Oceanfront Park has had the hottest sand so far, in the range of 92 to 93 degrees, she said.
She noticed that nesting turtles on a North County beach with replacement sand from an inland mine were taking a couple of days longer to hatch than at other county beaches. She also discovered that the sand was cooler than the original sand dredged from offshore.
“The temperature may not be a big deal,” Martin said, “but we need to know that we’re not altering the sex ratio a whole lot.”
County environmentalists are also analyzing sand composition and other factors, such as climate change, which may be making the beaches hotter. Cooler inland sand may be an inadvertent benefit.
“There are so many variables we have to consider,” Martin said. The county will bring in a statistician and the staff will spend six months to a year to analyze the data.
The project is being paid for with a $14,000 grant from sea turtle license plates.
So far this turtle season, the numbers of nests have been excellent, she said.
“Loggerheads have been numerous with some beaches getting record numbers,” Martin said. “Green turtles are having a phenomenal year with numbers exploding in the last two years.”
The high numbers are likely due to conservation efforts put in effect two decades ago, she said.